Treatment of cotton fibers



latented Oct. is, 1945 2,387,058 TREATMENT or oo'r'ron FIBERS Elmer-J. Cerny, Akron, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application October 6, 1942, Serial No. 460,985

4 4 Claims. (C'l. 57-164) This invention relates to a method of treating cotton fibers whereby the tensile strength, elasticity and fatigue resistance of such fibers are remarkably increased and to the improved yarns, cords and fabrics prepared from such treated In cotton fabrics to be used for Such purposes as in the construction of pneumatic tires, belts, hose,- and other fabric-reinforced rubber products, as well as in a number of other mechanical applications, it is desirable that the yarns or cords composing the fabric possess high tensile strength, high density, low stretch but high elasticity, and that they be highly fatigue resistant, that is, resistant to repetitions and fluctuations of stress. Ordinary cotton yarns and cords prepared by spinning and twistin cotton fibers which have previously been subjected to the common cotton processes including ginning, baling, picking, carding, drawing, combing, slubbing and roving, do not possess these properties to an entirely satisfactory extent, and, accordingly, the art has devised various methods of improving cotton yarns and cords in these essential properties.

These prior methods, however, have all been applied to the twisted yarns and cords while the initial steps of processing the cotton-from the time it is inned until it is spun into yarn have remained substantially the same.

I have now discovered that greatly improved tensile strength, elasticity and fatigue resistance may be imparted to the individual cotton fibers prior to the time they are spun and twisted into yarns and cords by subjecting untwisted paralleled fibers to a prestressing process, and that these improvements in properties are retained by the individual fibers during spinning and twisting with the result that finished yarns and cords having greater tensile strength, greater elasticity and greater fatigue resistance than any previously produced yarns and cords are obtained. i

This invention accordingly comprises prestressing untwisted parallel cotton fibers by applying a tension thereto of less than their breaking strength and, if desired, spinning such prestressed fibers into yarns and twisting the yarns into cords for rubber reinforcement such as tire cords. In preferred embodiments of the invention the paralleled fibers are prestressed while wet, the tension employed to stress the fibers is of the order of to 90% and preferably from about 25 to 60% of their breaking strength and the tension is applied in a plurality of successive operations of short duration with intermittent releasing of the tension and drying of the fibers preferably under a tension slightly less than that used to stress the fibers.

The improvement in the properties of the individual fibers brought about by this process may best be illustrated by the following examples.

Example I I age, of about 1575 parallel fibers were prepared and were mounted vertically in steel grips, the distance between the grips being 1%" so that each individual fiber was firmly gripped. The tensile strength of a number of these bundles was determined by means of a Suter tensile testing machine and was found to average 12.5 lbs. The fatigue resistance of each fiber bundle wasalso determined by suspending a weight on the gripped fiber bundle and then allowing the bundle to be vibrated at room temperature until breakage of the fibers occurred. When the load was 3.5 lbs., the fibers in the bundles were found to break after an average vibration time of 3.8 hours while with a 4.0 lb. load the fatigue life was 0.7 hour and with a 4.5 lb. load the fatigue life was 0.3 hour.

Another series of bundles of identically the same characteristics was similarly mounted and the fibers were stressed by applying a tension of 3.5 lbs. (approximately 28% of the breaking strength) to the fiber bundles under a static con dition for minutes. The tension was then released'and the tensile strength and fatigue resistance of the fiber bundles determined. It was found that the prestressed fibers P ssessed a hi her tensile strength than the original fibers and that, when vibrated under a 3.5 lb. load, breakage of the fibers did not occur until a vibration time of 29.2 hrs. had elapsed, an increase in fatigue life of over 700% as compared to fibers which had not been prestressed.

In another series of tests identical with the above except that a tension of 5.5 lbs. (44% of breaking strength) was applied to the fiber bundles for only 30 seconds, the tension released and the fibers then immediately vibrated under a 4.0 lb. load, the average fatigue life was 13.7 hrs., an increase of over 1900%. In similar tests in which the fibers were allowed to recover for a period of 70 hours between tensioning and vibrating under load, it was found that the average fatigue life was further increased to 26.3 hours or an increase of over 3700%.

It was also observed that after the tensioni process the fibers acquired a permanent set becoming more elastic while their stretch was reduced to that of about two-thirds of the ori inal fibers.

Example II Fiber bundles of the same characteristics as described in Example I were wetted by immersing them in an aqueous medium and then while still wet were vertically mounted and subjected to a 53 A series (Series 1) of cotton fiber bundles of the same type as described in Example I was wetted with water and then tensioned under a 3.5 lb. load for 5 minutes; a second series (Series 2) was immersed in a 1% aqueous solution of Triton W-30, a commercially available wetting agent, and while still wet was then tensioned under a. 3.5 lb. load for 5 minutes and a third series (Series 3) of bundles was similarly wetted with a solution of Triton W-30 and then tensioned under a 5.5 lb. load for 30 seconds. The fiber bundles in each The tension was re-* series were allowed to dry and were then vibrated under a. 4.5 lb. load until breakage.

The average fatigue life of the fibers in the three series together with the relative life as compared to a control in which the fiber bundles were tested without being wetted and tensioned is shown as follows:

Relative fatigue life (control =1.0)

Average istigue life hours Series 1. Series 2.. Series 3.

for the Triton W-BO" in this example, thus 80 showing that the use of aqueous solution of wetting agents to wet the fibers prior to stressing is highly desirable.

Example IV A series of cotton fiber bundles of the same type used in Example I 'were gripped in the manner described in Example I and were then stressed under a 2.5 lb. load for 5 seconds, the tension released, stressed under a, 3.0 lb. load for 5 seconds and the tension released and finally stressed under a 3.5 lb. load for'5 seconds and the tension released. The fatigue life of the fibers subjected to this process of successive stressing with intermittent releasing of tension were found ,topossess twice as long a fatigue life and a higher tensile strength than similar fibers subjected to a. continuous stressing under a 3.0 load for 30 seconds.

Example V (1) Wetted with a 1% solution of a wetting agent. (2) Stressed while wet under a 3.5 lb. load for 5 seconds. (3) Dried under a 3.0 lb. load for 2 hours. (4) Again wetted with 1% solution of a wetting agent.

Stressed under a 4.5 lb. load for 5 seconds. Dried under a 3.5 lb. load for 2 hours. Conditioned in a standard atmosphere.

When these fiber bundles were tested it was found that the fatigue resistance of the fibers was considerably greater (over 3 times as long a fatigue life) than when the fibers were wetted, stressed and dried only once and also greater (over 20 times as long a fatigue life) than when the fibers were subjected to three successive tensioning operations with loads of 3.5 to 4.5 lbs. without intermittent drying of the fibers under tension. The tensile strength of the fibers was also considerably greater when the successive wetting, stressing, and drying process was applied to the fibers.

Example VI A series of fiber bundles of the type used in the previous examples were wetted, stressed while wet to about 50% of their ultimate strength, the tension released and the fibers dried and allowed to recover for 70 hours. The fatigue life of the fibers so treated was found to be about 10 times as long as that of similar fibers which were treated in the same manner except that they were not given the 70 hour recovery period.

The above examples demonstrate quite conclusively that the tensile strength and fatigue resistance of cotton fibers may be remarkably improved by prestressing untwisted individual fibers. They also show that greatest improvements in fatigue resistance are obtained when the fibers are wetted, preferably with an aqueous solution of a wetting agent, before stressing, and allowed to dry under tension after stressing; when the tension applied for stressing is about 25 to of the breaking strength of the fibers, and when a plurality of successive stressing operations with intermittent releasing of the tension and drying of the fibers (if stressed while wet) is employed.

Although the method of the invention as illustrated by the above examples was applied to small bundles of individual cotton fibers, it is to be understood that the examples are. given merely to illustrate the improvements in the properties of the fibers themselves and that in commercial practice the invention may be carried out in a somewhat different manner but with the same excellent results.

Thus, in commercial practice it is most convenient to stress the cotton fibers while in the form of a sliver in which the fibers are substanin such a. sliver, as well as the wetting of the. fibers prior to stressing and drying after stressing if these expedients are performed, may be accomplished in a number of different ways and in a number of different types of apparatus, it being understood that the carrying out of my process is not dependent upon any particular form of apparatus.

One convenient and eflicient type of apparatus for stressing the individual fibers while in the form of a combed and drawn sliver is quite similar to a conventional drawing frame with the important exception that the distance between successive pairs of rolls must be less than the. fiber length of the cotton being treated. Thus, the apparatus may consist of a plurality of pairs of metallic or leather covered rolls spaced less than about inch apart (most high quality cotton possesses a fiber length of more than inch) together with weights suspended from the top rolls,

running the second pair of rolls at a slightly greater speed than the first or front pair of rolls. Similarly each succeeding pair of rolls may be made to run at a slightly greater speed or the same speed so that the fibers may be continuously stressed or stressed and released throughout the passage of the sliver between the rolls.

The amount of tension to be applied to the fibers of any given sliver may be determined by testing the strength of the sliver and may then be regulated by suitably adjusting the size of the weights suspended from the rolls and the relative speeds of the rolls. In this way it maybe insured that the preferred expedient of applying a tension equal to about to 65% of the breaking strength is effected.

Furthermore, by attaching to the apparatus conventional means for wetting the sliver prior to passing the sliver between the rolls, by regulating the speed at which the sliver is passed through the rolls and by passing the sliver between the rolls a plurality of times, it is easily possible to carry out the process according to the other preferred embodiments of stressing the fibers while wet and then allowing them to dry under tension and of subjecting the fibers to a plurality of successive stressing operations with intermittent releasing of the tension and drying of the fibers.

As an example of the practice of the invention on a commercial scale, a sliver of combed and drawn cotton fibers having a fiber length of about inch was passed through two successive pairs of rolls, the spacing between the rolls being inch and the weighting on the rolls being 10 lbs. The speed of the front rolls was 26 revolutions per minute while that of the back pair of rolls was 1.11 time as fast. Under these conditions the fibers were stretched about -50% of their ultimate elongation during each pass through the rolls. The sliver was passed through the rolls 5 times'and the tensile strength, elonga tion and fatigue resistance of the fibers then compared with that of the fibers in the original sliver. It was found that the treatment had improved the tensile strength of the fibers by over 5%, had lowered their stretch by about one-third and had increased the fatigue resistance by ten times.

In another. example theabove process was repeated except that the cotton sliver was wetted with a 1% aqueous solution of a wetting agent prior to each passing of the fibers through the rolls and was dried after each successive passing. In this instance an improvement of about 15% in tensile strength, a one hundred fold increase in fatigue resistance and a lowering of stretch of about two-thirds was effected.

The advantages of improved tensile strength,

elasticity and fatigue resistance of the cotton fibers treated in accordance with this invention are of great value to the textile art since the improved fibers may then be made into yarns, cords and fabrics which in turn are stronger, more elastic and more resistant to fatigue than similar articles made from ordinary cotton fibers.

The invention is particularly applicable to the.

manufacture of tire cords and other cords for reinforcing rubbery materials, by which is meant with natural and synthetic rubbers and other vulcanizable elastic materials, since it is especially desirable that such cords possess high tensile strength, be elastic so that they do not stretch and grow in service and possess high fatigue life so that they will resist the repeated fiexures encountered in service. Accordingly, fibers treated in accordance with this invention may be spun into yarns in the ordinary manner and a plurality of such yarns twisted into cords. Expedients commonly employed in the manufacture of tire cords such as wetting the yarns and twisting the wetted yarns into cords, stretching the yarns during twisting and stretching the finished cord maybe applied during the manufacture of cords from the improved fibers of this invention, the result being that these expedients still further improve the properties of the cord.

It should be mentioned, however, that the properties of the tire cords of this invention cannot be attained solely by expedients applied to the yarns or cords because of the fact that the pres-,- ent invention, in contrast to the methods known to the prior art, changes the structure of the individual fibers in such a way that the tensile strength and fatigue resistance of the fibers themselves are improved;

Having described my invention and preferred embodiments of the same it is my desire that the of rotating rolls, the said second pair of rolls being weighted substantially equally to the said first pair of rolls and being spaced from the said first pairof rolls a distance less than the length of the cotton fibers in the sliver so that the ends of the individual cotton fibers in the sliver are simultaneously gripped with substantially equal forces by the two pairs of rolls, and rotating the said second pair of rolls at a peripheral speed sufficiently greater than the speed of rotation of the said first pair of rolls substantially to stretch the individual cotton fibers in the sliver without breakage thereof, whereby to obtain a sliver of substantially the same thickness as the original sliver but in which the tensile strength and fatigue resistance of the individual cotton fibers is substantially improved. w

2. The method of claim 1 further characterized in that the cotton sliver is wetted before passing between the rolls.

a. The method of treating cotton which comprises arranging a multiplicity of untwisted cot-- ton fibers in a substantially parallel relation, gripthereof while the individual fibers are so gripped and without slippage oi the fibers from their gripped position, subsequently releasing the tension, and finally forming the stretched fibers into yarns whereby the tensile strength and fatigue resistance of the yarnsis substantially-improved.

4. The method of claim 3 further characterized in that the cotton fibers are wetted before applying tension thereto.

7 ELMER J. CERNY. 

